Electron discharge device



Jan. 7, 1958 T. M. SHRADER ELECTRON'DISCHARGE DEVICE 2 Sheets-Sheet 1 Filed April 5, 1956 INVENTOR.

Jan. 7, 1958 T. M. SHRADER ELECTRON DISCHARGE DEVICE Filed April 5, 1956 2 Sheets-Sheet 2 III) INVENTOR. 72kt) Mfiiwiz Terry M. Eihrader, Landisville, Pa,

poration of America, a corporation of Delaware 1956, Serial No. 576,395

The terminal fifteen years of the term of the patent to be granted has been disclaimed 1b (llaims. (Clu 315-3963) Application April 5,

relates to electron discharge devices, and more especially it relates to magnetrons.

A principal object of the invention is to provide a novel combination of cathode and grid structures for electron discharge tubes, particularly suited for use in magnetrons and the like.

Another object is to provide an improved magnetron having a series of discrete grid-controlled primary emitters which are especially shielded against back-bombardment by electrons.

Another object is to provide a grid-controlled magnetron having a series of discrete electron emitting cathode elements each housed in a respective anti-bombardment chamber, in conjunction with an individual grid for each cathode element also housed in the corresponding cathode compartment.

A feature of the invention relates to an electron discharge tube employing a series of discrete electron emitting cathodes each surrounded by a respective control grid, and with each cathode-grid combination being located within a respective recess in a common metal member, whereby all the cathodes and all the grids are shielded by said member against undesirable bombardment by high energy orbitally moving electrons.

A further feature relates to the novel organization, arrangement and relative location and interconnection of parts which by their mutual cooperation constitute an efficient high power grid-controlled electron tube, especially of the magnetron kind.

Other features and advantages will appear from the following descriptions and from the appended claims and attached drawing.

While the invention finds its primary utility as embodied in a magnetron tube, it will be clear that certain features of the invention can be equally well applied to other kinds of electron tubes.

Accordingly, in the drawing,

Fig. l is a side elevational view, partly sectional, of a magnetron embodying the invention. For clarity and simplicity in the drawing certain parts are omitted;

Fig. 2 is a 1 taken along This invention broken sectional view of Fig. the line Z-2 thereof;

Fig. 3 is a detailed view of part of the cathode anchoring and tensioning means of Figs. 1 and 2;

Fig. 4 is a detailed view of one of the cathode-grid units of Figs. 1 and 2;

Fig. 5 is a schematic'view of a magnetron embodying the invention.

As is well known, a magnetron usually comprises an electron emitting cathode surrounded by an anode which in one known kind of magnetron has a series of resonant cavities facing the cathode. By subjecting the electrons to a constant magnetic field transverse to the electron traiectors, the electrons are constrained to follow orbital or arcuate paths, and cooperate with the anode cavities to induce radio frequency voltages therein. A large percent of the emitted electrons leave the cathode in such a phase that instead of g'ving energy to the radio frequency field, they absorb energy therefrom and return to the cathode. These latter electrons bombard the cathode with sufiicient energy to cause undesirable effects, amongst which may be mentioned, useless dissipation of power at the cathode, destructive bombardment of the cathode surface, and ionization of the cathode material. These disadvantages are even more pronounced when it is attempted to modulate the intensity of the electron streams, for example, by the employment of an intervening control grid. Here again the back-moving electrons also bombard the grid, raising its temperature undesirably and even causing the grid to become a spurious emitter. The present invention provides a solution for the said difficulties, and permits of the construction of a high-powered magnetron either for pulsed oscillatory operation or for gridmodulated operation.

Referring to the drawing there are shown the cathode, grid and anode assembly of a magnetron. The cathodegrid unit is designated by the numeral 10, and the anode unit is designated by the numeralll. Merely for purposes of clarity in the drawing, the usual evacuated enclosing bulb or envelope of glass or other non-magnetic material is omitted from the drawing. Preferably, although not necessaril the magnetron is of the watercooled kind. The cathode assembly may include a tubular metal member 12 having a series of parallel longitudinal grooves or recesses 13 uniformly arranged around the external periphery thereof. In the particular tube illustrated, the member 12 has twelve such grooves.

Preferably, although not necessarily, each groove has a flat face 14 which extends approximately radially. The opposite wall of the groove, namely wall 15, is inclined at a suitable angle, for example sixty degrees, thus defining a somewhat V-shaped groove. if necessary each wall 14 may terminate in a flange 16 which extends short of the opposite Wall to define an electron emergence window 17 for each groove.

Suitably mounted in each groove in insulated space relation to the walls of the groove, is a cathode-grid unit. Each cathode of such unit may be in the form of an elongated flat metal ribbon or strip 18 and it may be surrounded by a respective foraminous or wire-wound control grid 19. Each cathode strip may be of the so-called directly heated kind, having its surface which faces the corresponding window 17 provided with a coating of any well known electron emissive material. If desired, each cathode element instead of being a flat ribbon, may be in the form of an elongated trough-like metal member with the trough packed with thoria or similar electron emissive material, in which case the trough may be covered with a perforated or foraminous cover, thus providing what is known as a cathode of the dispenser kind.

Each of the cathode elements at its upper end is supported from a metal ring 20 which in turn is fastened to a main tubular metal support 21 for the multiple unit cathode-grid assembly. Ring 20 has a series of twelve arcuate slots 22 through which pass the upper ends of the respective cathode elements. For the purpose of anshoring each cathode element so as to prevent it changing its planar relation with respect to its associated grid, the upper face of ring 20 is slightly undercut to provide oppositely disposed recesses into which fit the T-shaped tabs or lugs 23 on the respective cathode element.

Insulatingly attached to ring 20 by suitable bolts 24 is another metal ring 25. The two rings are insulated from each other by suitable insulating bushings 26, and insulating washers 27. The outer margin of ring 25 is of greater thickness than the inner margin and the latter is provided with a series of apertures 28 in alignment with the slots 22 to permit the passage of the respective cathin ring 32.

by the respective leaf springs 34 which bear against the members 30 urging the latter in a downward direction.

Brazed or otherwise oined to the upper end of member 12 is a metal ring 35 also having a series of openings into which are fitted the respective bushings 29. The outer margin of ring otherwise joined to Similarly brazed or The inner opening closure within member rings and 32 tition 39 and a of ring 32 is closed by a cup-shaped concentrically telescoped The space between member 12 and is divided into two parts by a tubular parmay be employed. In order to grid from its associated cathode element,

ilarly attached to ring 32. is another metal ring 49 into r which the lower ends of the various and to wl'zich they may be welded fastened so as to connect all the grids in parallel electri- Cally. A suitable lead-in member 50 can be connected to ring which ring is insulated in any suitable manner, for example by ceramic ring 51, from ring 32. It will be understood, of course, that any other suitable support means may be employed for insulatingly supporting the grids in their respective grooves in spaced relation to the respective cathode elements.

The various filament tensioning members can be connected in parallel by attaching the filament supports 39 to a metal cap member 52. The lower end of the cathode grid assembly it can be closed by the cup-shaped which may serve to connect the several members in parallel. cup-shaped metal member 53 closes at? the upper end of the assembly 10. it will be observed that the ing which is of larger diameter than the 21, so that member 21 is conductively connected through grid side-rods extend 1 recess in which it is ring 29 only to the upper ends of the cathodes 18. As shown in the schematic diagram of Fig. 5, the current for heating the various cathode elements can be connected over supply conductors (not shown) but connected to the members 211 and 44. A suitable probe or small picloup loop 54 can be insulatingly sealed through the wall of the evacuated enclosing bulb or container 55 and provided with a conventional coaxial connector 56. The grid coucan be connected to a suitable lead-in the pole-pieces electrons between magnetic field to orbital or arcu- Since the operation of magnetron devices is well known, suflice it to say that when the various cathode elements and would ordinarily move in somewhat linear trajectories towards the anode. However, when they are subjected to the magnetic field from the pole-pieces 53, 59,

electrical and dimensional parameters are chosen so that as many of these orbital electrons as possible induce high frequency currents in the associated resonant cavities formed by adjacent ribs. By reason of the construction hereinabove described, the electrons are prevented from bombarding the cathodes and grids in the successive grooves. If desired, the walls of each groove may be treated in any well known manner to reduce the likelihood of secondary electron emission therefrom.

Various changes made in the disclosed embodiment without departing from the spirit and scope of the invention.

What is claimed is:

1. A magnetron comprising a plurality of discrete elc"- tron emitting cathodes, a corresponding plurality of dis crete grids one for each cathode, generally circular anode means for said grids and cathodes and surrounding them in spaced relation, a shield for all said cathodes and grids, recesses in each of which is insulatingly mounted a corresponding cathode anode means, each of said recesses in said shield defining an electron emergence window facing the anode and the walls of each recess being oriented to shield both the cathode and grid therein from electron bombardment.

2. A magnetron according to claim 1 in which said cathodes are oriented so as normally to emit electrons in to said anode means.

recess, and means to support each cathode and grid in each recess with such orientation that the cathode normally tends to emit electrons in a non-radial direction with respect to said metal body, and anode means surrounding said cathodes and grids in spaced relation thereto.

4. A high powered electron tube according to claim 3, in which each of said recesses has a plurality of fiat side walls and each cathode has a substantially planar emitting surface substantially facing one side wall of the mounted, each recess having an electron emergence window facing said anode means.

ode and grid are located.

6. A high powered electron tube according to claim 5, in which each cathode is in the form of a flat metal strip and is insulatingly mounted within its respective recess in said metal body so that its plane is substantially radial with respect to said anode means.

7. A magnetron comprising a plurality of discrete elongated cathode elements, a plurality of grid electrodes one for each cathode element, a shield member having a plurality of elongated grooves in its external surface and within each of which is mounted a corresponding cathode and grid, anode means surrounding said cathodes and grids, means for providing a magnetic field parallel to said cathode elements to cause electrons emitted by said cathode elements to follow arcuate paths in the space between said cathode elements and said anode means, and means including the walls of said grooves for shielding each cathode and grid from electron bombardment by electrons returning to said cathode elements and grid electrodes along said arcuate paths.

8. A magnetron comprising a hollow anode, a cathodegrid assembly mounted within said anode and comprising a plurality of discrete cathode elements, a corresponding plurality of grid electrodes one for each cathode element, a single support member having a plurality of discrete recesses, and means insulatingly supporting each cathode and grid within a respective recess.

9. An electron discharge device comprising a plurality of discrete electron emitting cathodes, a corresponding plurality of discrete grids one for each cathode, anode means for said grids and cathodes and surrounding them in spaced relation, a shield for all said cathodes and grids, said shield having a plurality of discrete recesses in each of which is insulatingly mounted a corresponding cathode and grid with the cathode oriented therein so as normally to emit electrons in the space between the cathodes and anode means, each of said recesses in said shield defining an electron emergence window facing the anode and the walls of each recess being oriented to shield both the cathode and grid therein from electron bombardment, each of said cathodes is in the form of an elongated member having an electron emissive surface facing a side wall of the recess in which it is located.

10. An electron discharge device comprising a plurality of discrete electron emitting cathodes, a corresponding plurality of discrete grids one for each cathode, anode means for said grids and cathodes and surrounding them in spaced relation, a shield for all said cathodes and grids, said shield having a plurality of discrete recesses in each of which is insulatingly mounted a corresponding cathode and grid with the cathode oriented therein so as normally to emit electrons in the space between the cathodes and anode means, each of said recesses in said shield defining an electron emergence window facing the anode and the walls of each recess being oriented to shield both the cathode and grid therein from electron bombardment, each of said recesses is in the form of an elongated groove having side walls, and each of said cathodes is in the form of a metal strip carrying an electron emissive surface facing one side wall of its recess.

2,537,923 Overbeek Jan. 9, 1951 

